Description
This suggestion has a few pieces:
- Implement boolean literal types for
trueandfalse, in a fashion similar to Singleton types under the form of string literal types #1003 - Implement type guards for booleans. Essentially, control flow constructs like if-else, while, for, etc would be subject to a type guard if their guard expression is a boolean.
- Now we can update generators to have a
nextmethod that returns{ done: false; value: TYield; } | { done: true; value: TReturn; }, where TYield is inferred from the yield expressions of a generator, and TReturn is inferred from the return expressions of a generator. - Iterators would return
{ done: false; value: TYield; } | { done: true; value: any; }to be compatible with generators. - for-of, spread, array destructuring, and the type yielded by
yield*would only pick the value associated with done being false. - The value of a
yield*expression would pick the value associated with done being true. - Introduce a Generator type that can be used to track the desired type of a
yieldexpression. This would be TNext, and would be the type of the parameter for the next method on a generator.
The generator type would look something like this:
interface Generator<TYield, TReturn, TNext> extends IterableIterator<TYield> {
next(value?: TNext): IteratorYieldResult<TYield> | IteratorReturnResult<TReturn>;
throw(exception: any): IteratorYieldResult<TYield> | IteratorReturnResult<TReturn>;
return(value: any): IteratorYieldResult<TYield> | IteratorReturnResult<TReturn>;
[Symbol.iterator](): Generator<TYield, TReturn, TNext>;
[Symbol.toStringTag]: string;
}